Vliv diagenetických procesů na asociaci těžkých minerálů v pískovcích z lokality Slivotín (ždánická jednotka, flyšové pásmo Vnějších Západních Karpat, Česká republika)

Abstract

An electron microprobe study of polished sections prepared from a sample of fine-grained sandstone from the locality Slivotín (Ždánice-Hustopeče Formation, Ždánice Unit, Flysch Belt of the Outer Western Carpathians, Czech Republic) allowed to yield in addition to data on chemical composition also the detailed information on in situ textural relationships of individual minerals. During our study, emphasis was given to accessory phases belonging to the translucent heavy mineral fraction. The detrital garnet (Alm36-82Grs2-45Prp2-22Sps0-15) was extensively dissolved and replaced by calcite cement from its margins and along the cracks. Detrital fluorapatite was dissolved in a similar way, however, dissolution episode was followed by growth of authigenic rims composed of carbonate-fluorapatite. Other observed heavy minerals (zircon, chrome spinel, TiO2 phase, monazite, tourmaline) probably remained unaltered by diagenetic processes. The chemical composition of chrome spinels varies mostly between magnesiochromite and chromite, whereas spinel is very rare. The chemical composition of garnets and chrome spinels is comparable with published data from Czech, Polish and Slovak parts of the Flysch Belt of the Western Carpathians, and indicates the primary source of detrital material in rocks of deeper parts of orogen, characterized especially by the presence of catazonal metamorphites and almost lacking volcanic rocks. Redeposition of heavy minerals from older sediments cannot also be ruled out. The pronounced diagenetic alteration of garnet, if not very scarce in the area of Flysch Belt, could help to explain the earlier observations of wide fluctuations of contents of garnet in heavy mineral concentrates.

Neobvyklá asociace minerálů s willemitem z prostoru centrální části příbramského uran - polymetalického revíru (Česká republika)

“…Pozoruhodným jevem, který podle našich dosavadních znalostí zatím nemá v příbramském revíru obdoby, je masivní nahrazování křemene mladšími silikáty (nejprve willemitem a později hisingeritem). Rozsáhlejšího rozpouštění křemene lze dosáhnout buď působením vysokoteplotních fluid (cca 200 -420 °C;Leroy 1978;Poty et al 1986;Charoy, Pollard 1989;Bobos et al 2005) a/nebo alkalických roztoků (Fiala, Čadek 1981;Dolníček et al 2014;Dolníček et al 2022). Zatímco v rané fázi vývoje žíly (při zatlačování křemene willemitem) nelze vyloučit působení vysokoteplotních fluid (siderity v příbramské oblasti vznikaly za teplot 200 -300 °C; Žák, Dobeš 1991; Dolníček et al subm., Ulmanová et al subm.…”

Remobilization of HFSE, Y, and REE during Diagenetic Alteration of Heavy Minerals in Sandstones from the Chvalčov Site, Flysch Belt of the Outer Western Carpathians, Czech Republic

“…As well, the heavy minerals were frequently studied in the sandstones of the Flysch Belt of the Outer Western Carpathians. In this area, the early works dealt with the evaluation of assemblages of translucent heavy minerals, whereas the more recent papers were also focused on the determination of the chemical composition of selected provenance-specific mineral phases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], namely garnet [1,2,[5][6][7]9,12,14,15], tourmaline [5,7,9,11,13], apatite [14,15], monazite [5], amphibole [11], pyroxene [11], and chromspinels [5,7,8,[10][11][12]14,15]. A majority of these works identified similar compositions of translucent heavy mineral assemblages in sandstones from typical flysch successions, with garnet, zircon, and rutile as main minerals, in places with more significant contents of amphibole and/or tourmaline.…”

“…Only refs. [14,15] used another methodological approach based on in situ electron microprobe investigation of heavy minerals in polished sections prepared from untreated sandstone samples. These investigations yielded textural evidence of the diagenetic alteration of many detrital mineral phases.…”

“…Furthermore, refs. [14,15] showed that quartz, feldspars, garnet, apatite, and in some cases also monazite and zircon underwent variably intense diagenetic dissolution, which could be (as in case of apatite) followed by the growth of newly formed authigenic rims. In addition, refs.…”

“…In addition, refs. [14,15] reported abundant complete pseudomorphs of a TiO 2 phase after a Ti-bearing detrital phase. The only minerals that did not exhibit any signs of diagenetic alteration were muscovite and chrome spinel.…”